This invention relates to a mask blank providing system, a mask blank providing method, a mask blank transparent substrate manufacturing method, and a mask blank manufacturing method that can assure optical characteristics of a mask blank transparent substrate and a mask blank, and further relates to a mask manufacturing method that can prevent a pattern defect of a transfer target.
In recent years, following the miniaturization of semiconductor devices, reduction in wavelength of exposure light sources has proceeded so that the exposure wavelength has reached 200 nm or less. As such exposure light sources, proposal is made of, for example, an ArF excimer laser (wavelength: 193 nm) and a F2 excimer laser (wavelength: 157 nm). Shield films (light shielding films, opaque films) and phase shift films for shielding light and changing phases with respect to those exposure wavelengths have been rapidly developed and various film materials have been proposed (see, e.g. JP-A-2002-162727 and JP-A-2003-280168).
Further, several proposals have been made of manufacturing methods that suppress variation of optical characteristics (e.g. transmittance and phase difference) with which problems are expected in formation of those films (see, e.g. JP-A-2002-90978). Thus the variation of optical characteristics of the films has currently been suppressed.
However, upon measurement of the optical characteristics (transmittance, reflectance, etc.) of manufactured mask blanks, a problem has arisen that those mask blanks not satisfying a specification relating to variation of optical characteristics are included at a certain rate.
Further, when a mask pattern formed on a mask is transferred onto a transfer target to thereby form a transfer pattern by the use of an exposure system, a problem has arisen that the transfer target is subjected to occurrence of a pattern defect while no pattern defect is found in the mask pattern formed on the mask.
The present inventors have attempted to locate a cause for those problems from various aspects and found out that they are caused by transmittance variation in a transparent substrate of a mask blank due to absorption by the transparent substrate itself which has not conventionally been put in question.
Hereinbelow, description will be made in detail about the reason why the mask blank deviating from the specification relating to the variation of optical characteristics is manufactured and the reason for the occurrence of the transfer pattern defect, respectively, which have been learned from researches by the present inventors.
Currently, synthetic quartz glass is used as a material of a substrate of a mask blank which is adapted for use of the ArF excimer laser as an exposure light source and which is under rapid development. This synthetic quarts glass is also used as a material of a substrate of a practically used mask blank adapted for use of a KrF excimer laser as an exposure light source. The exposure wavelength of the KrF excimer laser is 248 nm. Therefore, even if there is manufacturing variation in synthetic quarts glass, the transmittance (transmittance in a plate thickness direction) is 88% or more (wavelength λ: 240 nm) with the 6025 size (plate thickness: 6.35 mm), which thus has been out of question.
However, when the wavelength of the exposure light source decreases to a short wavelength like 193 nm, the transmittance (transmittance in a plate thickness direction) sometimes decreases to 80% with the 6025 size (plate thickness: 6.35 mm) due to absorption by the substrate itself with respect to the exposure light caused by manufacturing variation in synthetic quartz glass and so on.
Further, in the present state, the manufacturing variation in the thin film formation is not completely overcome. It is thus presumed that the mask blank not satisfying the specification relating to the variation of optical characteristics as described above is manufactured due to synergistic action of the variation of substrate material transmittance and the variation of thin film optical characteristics.
On the other hand, with respect to a mask, a region where the transmittance is reduced due to the absorption by the synthetic quartz glass substrate itself does not exert an influence upon a transfer target when such a region is included in a shield film pattern region. However, when such a region is exposed in a region where a mask pattern is not formed, or when such a region bridges portions of the mask pattern, a portion where exposure light should not be shielded is resultantly shielded to thereby cause a change in intensity of the exposure light with respect to the transfer target. This is presumed to be the cause that generates the pattern defect in the transfer target although no pattern defect is found in the mask.
In recent years, mask patterns have been becoming much finer and more elaborate. Therefore, even if a defect that affects pattern transfer onto a transfer target can be identified on a mask, pattern alteration or correction cannot be often performed and. In this case, it is necessary to newly manufacture a mask from the beginning.